Increased Cycle Life Research Articles

PV-fed multi-output buck converter-based renewable energy storage system with extended current control for lifetime extension of Li-ion batteries

Recently, there has been a visible intensification of research on increasing the cycle life of energy storage devices used in Photovoltaic (PV)-fed energy storage systems (ESS). Compared to existing battery technologies, Lithium-ion (Li-ion) batteries have advantages such as high energy density and high cycle life. However, many existing Hybrid energy storage system (HESS) suffers from the fact that Li-ion batteries have limited cycle life, calendar and cycle aging. Therefore, attention has shifted towards the charging techniques necessary to improve the service life of Li-ion batteries by increasing their cycle life and reducing capacity losses. One such approach is to charge the battery by gradually increasing it from a certain level, rather than starting the charging process directly with the maximum charging current. This study proposes Extended Current Control (ECC) to reduce battery capacity losses and extend service life in PV-fed HESSs. The maximum power point (MPP) of the PV module is provided by the Perturb and observe (P&O) algorithm via the supercapacitor (SC) converter, while ECC is performed via the battery converter. This approach requires less hardware, unlike optimization, rule, or filtering based techniques. Controlling the battery current over a large area protects the battery packs from high currents at the start of charge and reduces capacity losses by increasing cycle life. Compared to PV-fed ESS containing only battery packs, the proposed technique provides a 40 % improvement in battery charging current, an 8 % improvement in the converter duty ratio in reaching the MPP point, and a 31.69 % improvement in battery capacity fades.

Morphology Matters: Surface Properties Inform ALD Deposition and Subsequent Electrochemical Performance in Graphite Substrates

The physical properties of graphite, such as pore volume, shape, and crystallinity; are critical factors in determining the performance of a li-ion cell. These properties are determined by the graphite manufacturing process, which often terminates with a surface treatment process to optimize the morphology. Currently most surface treatments are done using a carbon pitch coating, which involves a high temperature, multi-step process. Coatings using atomic layer deposition (ALD) are, by comparison, less energy intensive and a more customizable approach to target specific physical properties leading to increased cycle life, higher coulombic efficiency, and better rate performance. In this work we will show how ALD coatings are optimized based on the graphite production process and resulting particle morphology. We will demonstrate that these optimized coatings will serve to reduce surface area, prevent graphite exfoliation, and improve li-ion diffusion pathways.

Interface engineering enabled by sodium dodecyl sulfonate surfactant for stable Zn metal batteries

Aqueous zinc-ion batteries are emerging as powerful candidates for large-scale energy storage, due to their inherent high safety and high theoretical capacity. However, the inevitable hydrogen evolution and side effects of the deposition process limit their lifespan, which requires rational engineering of the interface between anode and aqueous electrolyte. In this paper, an anionic surfactant as electrolyte additive, sodium dodecyl sulfonate (SDS), is introduced to deliver highly reversible zinc metal batteries. Unlike traditional surfactants, the solvation structure is not affected by SDS, which tends to adsorb on the (002) crystal plane of Zn with the purpose of effectively limiting the water molecules adsorption. Attributed to the natural hydrophobic part of SDS, a dynamic electrostatic shielding layer and a unique hydrophobic interface are constructed on the anode. Assisted by the above merits, the adverse surface corrosion, hydrogen evolution and dendrite growth are significantly inhibited without the sacrifice in the deposition kinetics of Zn ions. As a result, the Zn||Zn symmetric batteries demonstrate an increased cycle life of 2000 h (1 mA cm−2, 1 mA h cm−2) with the presence of SDS additive. Such strategy provides a new avenue for the developing advanced electrolytes to be applied in aqueous energy storage systems.

Identifying the origin of inhomogeneous degradation and irreversible swelling inside cylindrical 21700 high-energy lithium-ion cells

Cylindrical cells are gaining market volume in the production of batteries for electric vehicles among others due to high flexibility with regard to space utilization. However, the internal winding structure can be prone for inhomogeneities regarding current distribution, electrode degradation, and mechanical stress. In this study, 27 cylindrical SDI INR21700 50E cells with a nickel-rich NCA cathode and a Si/C composite anode were subjected to five individual aging procedures. Computed tomography scans were conducted at 100%, 90% and 80% capacity retention to investigate internal swelling and deformation of the jelly roll non-destructively. The cells were disassembled at 80% capacity retention for post-mortem analysis on coin half-cells harvested from different locations of the jelly roll to quantify inhomogeneous aging and electrode swelling.Increased cycle depth and discharge current exacerbated inhomogeneous degradation across the electrode length. In comparison to 860 equivalent full cycles (EFC) at 0.5C and 100% cycle depth, limiting the SoC range between 20% to 80% at 25°C increased cycle life to 4150EFC despite a high discharge current of 2C. Minimizing utilization of the silicon content and avoiding lithium plating, the cathode and the anode retained around 4% and 2% increased capacity at the inner winding area in comparison to the outer area, presumably due to increased mechanical pressure at the inner area. At the same time, the inner area displayed reduced swelling, further suggesting increased mechanical pressure at the inner area. Overall, the irreversible swelling measured 6% to 16% and 8% to 20% for the cathodes and the anodes after disassembly, depending on the operating conditions and the location on the electrode. To prevent non-linear capacity fade and deformation of the jelly roll, the results suggest to restrict utilization of the silicon content and to avoid high charging currents at low temperature.

Suitability of late-life lithium-ion cells for battery energy storage systems

The globally installed capacity of battery energy storage systems (BESSs) has increased steadily in recent years. Lithium-ion cells have become the predominant technology for BESSs due to their decreasing cost, increasing cycle life, and high efficiency. However, the cells are subject to degradation due to a multitude of cell internal aging mechanisms, which result in reduced capacity, efficiency, and usable nominal power range over a BESS life cycle. Towards their end-of-life, the cells often show a steep increase in their degradation rate, called nonlinear aging. This work investigates how these ”late-life” lithium-ion cells perform in typical BESS applications. We show how decreased capacity, efficiency, and nominal power range impact the profitability of a home storage system for self-consumption increase (SCI) and a large-scale storage system for energy arbitrage (EA). A physicochemical aging model, which accounts for lithium-plating-induced nonlinear aging, is developed and parameterized based on an experimental cell aging study. The aging study and model show that cells that have entered the nonlinear aging phase can transition back to a significantly reduced degradation rate through adapted operating conditions, namely a reduced charging rate and operating voltage window. The case study highlights that the battery cells enter the nonlinear aging phase significantly earlier when used for the EA application compared to the SCI application. However, by adapting the operating conditions below 80% state of health, the obtainable net present value over the investigated ten-year timeframe in the EA application increases by 39.8%, and the lifetime is significantly prolonged.

Heat dissipation performance research of battery modules based on composite phase change materials cooling and electrochemical thermal coupling model

In order to improve electric vehicle lithium-ion batteries (LIBs) performance and increase cycle life, it is crucial to design a reliable and efficient battery thermal management system (BTMS). Compared with other active battery cooling methods, passive phase change material (PCM) cooling has the advantages of simple structure, good temperature control uniformity, strong reliability, and no additional energy consumption. This article uses a series of experimental procedures to add expanded graphite to traditional paraffin wax PCM and obtain composite phase change materials (CPCM) with different mixing ratios. A control experiment is created to compare the cooling performance of the CPCM cooling with natural convection cooling, research shows that the cooling performance of CPCM can well meet the cooling demand which maximum temperature and maximum temperature difference of battery modules. In addition, to study the performance of thermal properties parameters related to CPCM, a COMSOL numerical calculation model of battery module based on CPCM cooling and electrochemical thermal coupling model is established. The effectiveness and accuracy of the model are verified through heat generation experiments at different rates (0.5 C, 1 C, 1.5 C), with a maximum temperature error of 1.6 K and an error accuracy of less than 0.6%. Subsequently, the performance of phase change temperature, thermal conductivity and phase change latent heat is studied and reasonable value ranges are obtained, which are 312 K∼318 K, 2.5 W /(m·K), and 175 J/g∼200 J/g, respectively.

Scaling a Gas Phase Residual Lithium Conversion Process on Ni-Rich NMC Cathode Materials in Commercial Fluidized Bed Reactors

‘Residual lithium’, the LiOH and Li2CO3 surface contamination that is ubiquitous to Ni-rich NMC manufacturing, is a significant obstacle in the large-scale production and handling of high-nickel layered oxides. These hydroxide and carbonate surface phases influence reproducibility and shelf stability of the NMC powder and cause gelation and particle aggregation during electrode casting. There is ample evidence in the literature that atomic layer deposition (ALD) possesses a two-fold solution to this problem.1-3 First, reactive organometallic species such as trimethylaluminum (TMA) can convert insulating residual lithium to a Li-rich LixAlyO conducting layer. Customizable ALD layers can then be added to inhibit the re-formation of the carbonate layer and to deter negative side reactions of the CAM surface with the liquid electrolyte. While highly impactful, these studies have mostly been relegated to small, lab-scale demonstrations of <50 g. As such, there remains a need to enable this ALD-assisted-technology for high-throughput commercial applications.In this talk, we will explore the progression of a residual lithium conversion process from lab (10 – 1000 mL) to industrial-scale (10 L – 100 L) fluidized bed equipment and how scale and material-dependent parameters can impact performance. Using a commercial NMC 811 cathode as a case study, we first applied aluminum phosphate ALD coatings on a lab-scale fluidized bed reactor to examine the interfacial and electrochemical changes of the CAM material under various process conditions. ICP-OES measurements confirmed linear and reproducible deposition versus ALD cycle number between 200- 300°C. XPS analysis showed the ALD coated NMC 811 powder had an 80% reduction in Li2CO3 versus the pristine material and that a reduction persisted even after 10 days of storage in atmospheric conditions. At standard (0.5C/1C) cycling to 4.4V, AlPO4 coatings increased cycle life by 44% versus the uncoated powder. Under optimized conditions, the process was scaled first to 1 kg and finally to 10 kg in a pilot-scale reactor. In-situ mass spectrometry indicated that residual lithium conversion byproducts such as CO2 could be used to monitor reaction progress and optimize chemical usage efficiency. Fluidization aids including vibration and mechanical stirring were used to inhibit and break up powder agglomerates. ICP-OES and electrochemical cycling data confirmed reproducible deposition and cycle life benefits versus the small scale runs and pristine materials, demonstrating a pathway for these ALD-enhanced materials to transition from lab-scale demonstration to viable product. We will discuss strategies for continuing the scaling process to 100 kg batches for commercial applications.[1] M. Young et al., The Journal of Physical Chemistry C 2019 123 (39), 23783-23790[2] P. Darapaneni et al., ACS Applied Energy Materials 2022, 5, 8, 9870–9876[3] J. Li et al., Coatings 2022, 12(1), 84

(Invited) Extending Cycle and Calendar Life of Si Based Li-Ion Batteries By Localized High Concentration Electrolytes

Si is one of the most promising anode materials for the next generation of lithium (Li) ion batteries (LIBs). Recently, we have developed a porous Si with a unique carbon coating structure (“carbon on Si” instead of “Si on carbon”). The nano-porosity of the materials absorbed most of volume expansion so the particles (between 3-5 mm) can retain their integrity during cycling instead of breakdown observed in bulk Si particles. Although single layer pouch cells (Si/NMC622, 62 mAh) with this porous Si anode and baseline electrolyte (1.2 M LiPF6 in EC-EMC (3:7 by wt.) +10 wt.% FEC) can retain 91% capacity after 800 cycles, their calendar life is still far shorter from 10-year target required by electrical vehicles.In this work, we present a systematic investigation of the application of localized high concentration electrolyte (LHCE) to extend the cycle life and calendar life of Si-LIBs. A typical LHCE contains a Li salt (typically LiFSI) with high solubility in a common solvent (such as DMC), and a diluent (such as TTE) with minimal solubility of the Li salt. Compared with other electrolyte design, one distinct advantage of LHCE is that solvent and diluent in LHCE can be largely decoupled from each other: change in once components will have not significantly affect the functionality of other components. This characteristic of LHCE enables much more freedom in the electrolyte designs to satisfy different practical application needs (such as long cycle life, long calendar life, high rate, high temperature, and high voltage). For example, Si/NMC622 cells with a composition of LiFSI-2.15DMC-0.17VC-0.69FEC-4.31TTE (in molar ratio) have increased cycle life of Si/NMC622 pouch cells to 2000 cycles with 80% capacity retention at 25°C as compared with 1000 cycles when baseline electrolyte was used. However, this electrolyte is less stable when LiCoO2 is used as the cathode, leading to rapid capacity loss at elevated temperatures (45°C). One possible reason for this is that cobalt in the cathode leads to more rapid decomposition of FEC than in the case of NMC622 at 45°C. On the other hand, the stability of LHCE is significantly affected by the amount of free (unbound) solvent (including DMC, VC, and FEC in the above example) in the electrolyte. By minimizing the amount of total free solvents, an electrolyte with a composition of LiFSI-2DMC-0.1EC-0.1FEC-3TTE has led to a long cycle life of Si/NMC622 cells at 25°C. Increasing the amount of main solvent in the electrolyte can further increase the conductivity of the electrolyte and significantly increase the charge/discharge rate of the cells.The long calendar life of Si-LIBs can be measured by accelerated tests at elevated temperatures (up to 55°C). Although FEC-containing electrolytes can increase the cycle life of Si-LIBs at room temperature, most Si-LIBs with FEC-containing electrolytes exhibit a rapid increase in impedance at elevated temperature, leading to a short projected-calendar-life. We designed a series of experiments to investigate the effect of FEC on the calendar life of Si-LIBs. The results clearly indicate that the formation of a high impedance interphase layer on the anode and cathode surfaces due to the decomposition of FEC at high temperatures is one of the fundamental reasons for the short calendar life of Si-LIBs. By replacing FEC with an alternative additive, a new LHCE electrolyte has been designed that led to much better cycling stability of Si-LIBs at 45°C (less than 5% capacity loss in 500 cycles) and much longer calendar life. More details of these investigations will be reported in this presentation.

Experimental Investigation of the Lithium Calendering Process for Direct Contact Prelithiation of Lithium‐Ion Batteries

Lithium‐ion batteries suffer from high initial capacity losses during formation. One possible approach to compensate for these initial capacity losses is prelithiation, which is the addition of lithium into the battery cell before formation. A promising method is direct contact prelithiation using lithium foil, which requires lithium foil thicknesses below 10 μm to ensure the safe and accurate performance of the prelithiation process. However, free‐standing lithium foils are only commercially available down to a thickness of 20 μm; hence, in this present work, the calendering process of lithium is investigated in detail. An already developed process model will be adapted to provide detailed information on the deformation properties and thickness reduction of different lithium foil thicknesses. A design of experiments is used to investigate the influences of lithium foil geometry, line load, web speed, and roller temperature on the deformation behavior of lithium during calendering. Lithium foil is applied onto anodes by calendering, which are electrochemically investigated using pouch cells. The cells prelithiated by calendering show improved electrochemical performance compared to the manually prelithiated cells, increasing cycle life by 19%.

Role of Acetonitrile Additive in Enhanced Performances of Aqueous Zn Anodes

Zinc-ion batteries have been proposed as promising candidates to address ever-growing demands for energy storage and limited resources available for the currently used lithium-battery systems. Despite their promise, the apparent advantages of aqueous zinc-ion batteries (low cost and high energy density) are still overshadowed by uncontrolled water interactions at the zinc metal-electrolyte interface, such as the hydrogen evolution reaction and electrode corrosion. A number of different strategies – e.g., water-in-salt, addition of chelating agents and/or co-solvents – have been proposed to overcome the aforementioned interfacial problems. Among them, the addition of acetonitrile to aqueous ZnSO4-based electrolytes has shown great promise, with reports of improved Coulombic efficiencies and increased cycle life. However, the actual role of this additive remains unclear. In this work, we determine the mechanistic principles behind the participation of acetonitrile in enhancing the performance of aqueous Zn batteries. For this purpose, we utilized a combination of X-ray absorption and Raman spectroscopies, cyclic voltammetry, and galvanostatic coin cell cycling. Our results indicate that the addition of acetonitrile perturbs the interfacial solvation structure, rather than the bulk. Specifically, acetonitrile does not penetrate the first solvation shell of the Zn2+ ion, but does modify interfacial solvation behavior, likely by physisorption to the electrode surface. The Coulombic efficiency of half cells was found to depend on electrode material, employed current density and capacity, and only moderately on acetonitrile concentration. Overall, this works points strongly to the need for systematic evaluation of battery performance in co-solvent systems, and provides a new framework for future efforts to optimize ion transport and performance in zinc-ion batteries._______________________The submitted manuscript has been created by UChicago Argonne, LLC, Operator of Argonne National Laboratory (“Argonne”). Argonne, a U.S. Department of Energy Office of Science laboratory, is operated under Contract No. DE-AC02-06CH11357. The U.S. Government retains for itself, and others acting on its behalf, a paid-up nonexclusive, irrevocable worldwide license in said article to reproduce, prepare derivative works, distribute copies to the public, and perform publicly and display publicly, by or on behalf of the Government. The Department of Energy will provide public access to these results of federally sponsored research in accordance with the DOE Public Access Plan. http://energy.gov/downloads/doe-public-access-plan

Performance Advances of Industrial-Design Rechargeable Zinc Alkaline Anodes via Low-Cost Additives

Cost and safety are emerging as paramount considerations for grid-scale energy storage and often limit battery technology from practical deployment. Zinc alkaline is under renewed interest due to opportunity for lowered cost and improved fire safety. Nominal industrial-design zinc alkaline electrodes need improvement on their ∼100 cycle life when cycled at significant zinc utilization. Here, we analyze a collection of 72 practical paste Zn alkaline electrodes at 15 or 30% utilization of zinc’s 820 mAh/g Zn, with and without additives, and compare the resulting performance, industrial cost, and material evolution. Additives comprising calcium hydroxide [Ca(OH)2], bismuth oxide (Bi2O3), cetyltrimethyl ammonium bromide (CTAB), and/or a synthetic layered silicate (Laponite) were chosen to reduce shape change, mitigate gassing, reduce zincate migration, and alter the ionic environment, respectively. The concentration of potassium hydroxide (KOH) was also varied (10, 20, and 37 wt % KOH). We find performance that surpasses the best values in the literature for practical, real-world, industrially relevant zinc alkaline electrodes: Ca(OH)2 with Bi2O3 increased cycle life to ∼1200 cycles in 20% KOH (150 Ah/mL anode volume); CTAB with Bi2O3 and Laponite in 10 wt % KOH achieved slightly higher than ∼1200 cycles (∼210 Ah/mL anode volume) and pure-ZnO electrodes in 10 wt % KOH cycled ∼1000 times at 15% Zn utilization (240 Ah/mL anode volume). XRD, SEM, and EDS characterization reveals an altered microstructure when the additives are used. The first direct observation of calcium zincate cycling is collected by in situ XRD. The characterization data suggest that the mechanism for increased cycle life is capture and localization of the soluble zincate that forms during discharge, thereby reducing zinc material dispersal and shape change and increasing cycle life. Another important feature is pore geometry. When Bi2O3 is added, the electrode microstructure switches from a “closed cell” pore geometry with large ZnO flakes locking up pores to a more “open cell” geometry when small amounts of Bi2O3 are present.

Delicately Designed Cyano‐Siloxane as Multifunctional Additive Enabling High Voltage LiNi0.9Co0.05Mn0.05O2/Graphite Full Cell with Long Cycle Life at 50 °C

AbstractLithium‐ion batteries (LIBs) adopting layered oxide cathodes with high nickel content (Ni ≥ 0.9) always suffer from extremely poor cycle life, especially at elevated temperatures and higher charging cut‐off voltages. Adding small amounts of functional additives is considered to be one of the most economic and efficacious strategies to resolve this issue. Herein, cyano‐groups are introduced innovatively into a siloxane to delicately synthesize a novel cyano‐siloxane additive, namely 2,2,7,7‐tetramethyl‐3,6‐dioxa‐2,7‐disilaoctane‐4,4,5,5‐tetracarbonitrile (TDSTCN). Encouragingly, 0.5 wt.% TDSTCN additive enables ultrahigh nickel LiNi0.9Co0.05Mn0.05O2/graphite (NCM90/Gr) full cells with dramatically increased cycle life, especially at an elevated temperature of 50 °C and a high charging cut‐off voltage of 4.5 V. The characterizations reveal that the TDSTCN additive can scavenge HF and promote the formation of robust stable interface layers on NCM90 cathode and Gr anode due to the synergistic effects of cyano‐groups and Si−O bonds. These results reveal the great significance of designing one single additive with several functional groups in enhancing the comprehensive electrochemical performances of high Ni LIBs.

Exploring the Effects of Dopamine and DMMP Additives on Improving the Cycle Boosting and Nonflammability of Electrolytes in Full-Cell Lithium-Ion Batteries (18650)

Concerns over recyclability, performance, and safety have grown as the use of commercial Li-ion batteries to meet our energy needs has increased. Electrolytes may aid in increased flammability, capacity loss, and safety. Dimethyl methyl phosphonate (DMMP), a flame retardant, and dopamine hydrochloride (DOP) are utilized to increase the cycle life and graphite anode compatibility. The optimal additive formulation (5% wt DMMP and 0.1% wt DOP) reduces inflammability and increases cycle life and reversible capacity (99.14%). Molecular dynamics simulations provide a comprehensive atomistic account of the dynamics of Li+ ion solvation in the electrolytes and in the presence of additives. Dopamine and DMMP increase the Li-ion solvation-free energy in the electrolyte formulation. While increasing the Li-ion conductivity, additive addition reduces the electrolyte viscosity and enables the formation of a smaller, stronger Li-DMMP-DOP complex than the larger Li-carbonate complex found in Li-neat electrolyte systems. When DMMP and DOP are added to the electrolyte, the carbonates are displaced from the Li-carbonate complex by these additives. The Li-ion solvating nature or compatibility was improved upon the addition of DMMP/DOP further aided by a faster diffusive behavior of the Li complex, which in part would be instrumental in enhancing the performance and safety of the battery electrolyte additive formulations. The modified electrolyte (DMMP 5% wt, DOP 0.1% wt) has a conductivity of 18.60 mS cm–1 and a low viscosity at 25 °C. This formulation was evaluated using graphite/NMC-532 cylindrical cells with commercial electrodes. The performance of the graphite/NMC-532 cells containing the modified electrolyte was comparable to those of regular electrolytes based on carbonates: ethylene carbonate/dimethyl carbonate/ethylmethylcarbonate (EC/DMC/EMC) (1:1:1) additions. These findings indicate that DOP and DMMP have a lower oxidation potential (4.3 V) than most commercial electrolytes (4.5 V), preventing cathode deterioration. These insights should pave the path for rational design of practical and cost-effective Li-ion battery electrolyte additive combinations aimed toward lower flammability and improved performance.

Li-ion complex enhances interfacial lowest unoccupied molecular orbital for stable solid electrolyte interface of natural graphite anode

To increase cycle life and reduce costs for natural graphite anode, graphite tailings grafted with polyether amine (PEA) is prepared for artificial solid electrolyte interphase (SEI). The complex of PEA and Li+ has a well-tuned lowest unoccupied molecular orbital (LUMO) energy (0.216 eV∼-0.239 eV) to improve the chemical stability of SEI components, effectively hinders electron transfer from anode to electrolyte, and inhibits electrolyte decomposition. Meanwhile, the strong adsorption between Li+ and PEA enhances the de-solvation ability of SEI, thus improving the rate performance of the anode. After 1000 cycles, the capacity retention of the anode material with grafted PEA molecular weight of 2000 is increased from 22% to 98%. The method can also improve rate performance for graphite anode, with the capacity retention rate at a current density of 1 A g−1 (vs. 0.1 A g−1) increasing from 42% to 72%. As expected, the full cell life with LiFePO4 as the cathode material is significantly extended, the capacity retention improved from 44% to 77% after 200 cycles.

A KMnO4-Generated Colloidal Electrolyte for Redox Mediation and Anode Protection in a Li-Air Battery.

The rechargeable lithium-oxygen (Li-O2) battery has the highest theoretical specific energy density of any rechargeable batteries and could transform energy storage systems if a practical device could be attained. However, among numerous challenges, which are all interconnected, are polarization due to sluggish kinetics, low cycle life, small capacity, and slow rates. In this study, we report on use of KMnO4 to generate a colloidal electrolyte made up of MnO2 nanoparticles. The resulting electrolyte provides a redox mediator for reducing the charge potential and lithium anode protection to increase cycle life. This electrolyte in combination with a stable binary transition metal dichalcogenide alloy, Nb0.5Ta0.5S2, as the cathode enables the operation of a Li-O2 battery at a current density of 1 mA·cm-2 and specific capacity ranging from 1000 to 10 000 mA·h·g-1 (corresponding to 0.1-1 mA·h·cm-2) in a dry air environment with a cycle life of up to 150. This colloidal electrolyte provides a robust approach for advancing Li-air batteries.

Developing ester-based fluorinated electrolyte with LiPO2F2 as an additive for high-rate and thermally robust anode-free lithium metal battery

The electrolyte of 1 M LiPF6 in FEC/TTE/EMC (FTE 352) has been demonstrated to increase cycle life, safety, and energy density of anode-free lithium metal battery (AFLMB) due to its high oxidative stability, nonflammability, and capability to form lithium fluoride (LiF) rich solid electrolyte interphase (SEI). Methyl acetate (MA), a linear ester, is selected to reduce the use of expensive FEC and expand the adaptability of an electrolyte for high rates and lower temperature applications. Due to its lower LUMO value, a complementary additive LiPO2F2 was applied to tune the SEI. In this work, 1 M LiPF6 in FEC/TTE/EMC/MA (1/5/2/2 vol ratio) + 1 wt% LiPO2F2 was thus developed, which has high ionic conductivity, high oxidative stability (>5 V), high-rate capability, thermal stability, and tolerance to low temperature (0 °C). Using an anode-free configuration, this electrolyte delivers an average coulombic efficiency of 97.5% at room temperature and 96% at 0 °C. In contrast, the average coulombic efficiency of 1 M LiPF6 in FTE 352 is 94.4% at 0 °C. This electrolyte also holds capacity retention of 48% under a current density of 2 mA/cm2 using Cu||NMC111, while the reference electrolyte's capacity retention is 35%.

A Robust Bundled and Wrapped Structure Design of Ultrastable Silicon Anodes for Antiaging Lithium-Ion Batteries

Silicon with its high theoretical specific capacity for Li-ion storage has long suffered from its huge volume expansion and low intrinsic electronic properties, leading to poor rate performance and cycling stability. Recently, considerable efforts have been placed on achieving increased cycle life using nanomaterial structuring approaches. However, finding an efficient strategy to realize high capacity with a long cycle life of Si anodes is still a great challenge. In this work, a novel multileveled design of a web-like morphology is reported as a highly stable 3D interconnected Si network. This heterostructure of nano-sized Si (nSi), nitrogen-doped carbon nanotubes (N-CNTs), and graphenized polyacrylonitrile (g-PAN) is prepared via a low-cost method as an anode for LIBs. This sturdy composite integrates the individual benefits from each of its components, where nSi delivers high energy storage capacity, N-CNTs with nitrogen functionalization act as electron highways and flexible networks to connect nSi particles, and g-PAN produces nitrogen-doped graphene sheets wrapped around the entire electrode structure and buffers the volume change during lithiation. We found that only when all three components are present that significant enhancements in performance are observed. Specifically, this heterostructure exhibits excellent stability with a reversible capacity of ∼1370 mAh g–1 over 1100 cycles at a high current rate of 3000 mA g–1. Moreover, high loading cycling of up to 3 mAh cm–2 at ∼1 mgSi cm–2 was achieved at 500 mA g–1. This effective strategy introduces a promising avenue for the scalable production of high-performance next-generation LIBs.

An Initial Exploration of Coupled Transient Mechanical and Electrochemical Behaviors in Lithium Ion Batteries

While lithium-ion batteries are the dominant technology in the energy storage market, aspects of these batteries remain a mystery. For example, better understanding of chemical and mechanical crosstalk, and transients thereof, may lead to increased cycle life and rate capability. Here, an ultrasound acoustic characterization technique is introduced to probe the electrode/electrolyte interface in operando using signal amplitude analysis. This technique gives insight into lithium-ion concentration accumulation and depletion at the electrode/electrolyte interface, and these findings are consistent with Dualfoil model simulations.

Composites As High Energy Density Anodes for Li-Ion: Si/Graphite Vs. Si/Amorphous C/Rgo

High energy density anodes for Li-ion technology are the next step to achieve battery-based electric transportation with longer driving range. The substitution of graphite by Si-based materials could lead to a 20% improvement on the volumetric energy density of the battery, from 700 Wh/L (graphite anode) to 900 Wh/L (Si-based anode). However, Si anodes present some problems that must be solved in order to achieve generalized commercial market acceptance. The huge volume change that Si undergoes when alloying with lithium (about 300%) causes electrode cracking and pulverization and limits the cycle life of the electrode. This work compares the efficiency of two different Si-based composites to prevent electrode degradation and enhance the cycle life.Both composite materials were prepared with similar proportions of the same Si nanopowder (~100 nm) supplied by Tekna[1]. The first sample consists in a mixture of Si nanopowder with graphite, whereas the second material comprises Si/amorphous carbon/reduced graphene oxide (rGO). The synthesis process of the latter sample includes the mixture of Si nanopowder with an organic carbon source in a water-based suspension of graphene oxide that is subsequently annealed in inert atmosphere at 900º C. Structural and morphological characterization of the prepared materials includes X-ray diffraction (XRD), scanning electron microscopy (SEM) and Raman spectroscopy. The degree of order present in the carbon of the samples was obtained from XRD and Raman spectroscopy. The comparison of these data showed the very different nature of the carbon in both composites; graphite was significantly ordered while the carbon generated from an organic source was much closer to a hard carbon. Analysis of the SEM images showed the distribution of Si nanoparticles in the carbonaceous matrix (graphite or amorphous C/rGO).Electrochemical galvanostatic tests were also performed in 2032 coin cells in half cell configuration vs. metallic lithium at C/3 rate for 150 cycles. Initial coulombic efficiency at C/20 formation cycle and specific capacity, cycle life and capacity retention were examined for both composite materials (Fig. 1). The differences found in the electrochemical performance between the two composites were related to the observed structural and morphological features of the carbonaceous fraction. The high initial capacity loss observed (53 %) for the Si/C/rGO composite and the substantially low electroactivity of this carbonaceous fraction (vs. specific capacity of 350 mAh/g for graphite) hindered the overall energy density of this composite anode electrode. On the other hand (Fig.1c), the Si/C/rGO electrode retained above 99% of the initial specific capacity after 150 cycles at C/3 (2190 mAh/g-Si) in comparison with 65% capacity retention for the Si/Gr anode (421 mAh/g-Si/Gr) with equivalent low Si content (10 wt%). These preliminary findings on increased cycle life by the preparation of Si/C/rGO materials will be applied to higher Si content composite anodes. [1] http://www.tekna.com/ Figure 1 . Formation cycle voltage profiles at C/20 current rate for the (a) Si/Gr and (b) Si/C/rGO anode electrodes with low Si content (~10 wt%). Capacity retention (c) at C/3 cycling. Figure 1

(Invited) Extend Calendar Life of Si Based Li-Ion Batteries

Although significant progress has been made in increasing the specific energy and cycle life of silicon (Si) based Li-ion batteries (Si-LIBs), calendar life of these batteries is still less than two years, which is far less than the 10 year life-time required for electrical vehicle applications.1 Graphite anodes undergo only ~10% volume change during cycling, so SEI formed during the initial process does not experience significant mechanical stress during the subsequent cycles. However, the SEI layer formed on Si anodes experiences tremendous mechanical stress during repeated cycles. Most SEI layers formed on the Si surface in conventional electrolytes break down, exposing fresh, lithiated Si or SiO to electrolyte. Thus, significant Si corrosion and electrolyte consumption continuously occur during battery storage, especially in the fully lithiated conditions and elevated temperatures required for the accelerated calendar life test.2 As a result, the impedance of the Si anode will increase much faster than a graphite anode and shorten its calendar life, as observed in nearly all Si-LIBs. In this work, we will report the results of our recent investigation on the fundamental mechanism behind the limited calendar life of Si-LIBs. Several approaches that alleviated degradation of SEI layer and increasing cycle life of Si-LIBs will be discussed, including the nanostructured Si designs that can minimize the external size expansion, minimized particle surface area, and formation of stable SEI layers by localized high concentration electrolyte tailored for Si anode. The combination of these methods can largely extend the calendar life of Si-LIBs and accelerate the application of these batteries for large-scale electrical vehicles and consumer electronics applications.